Modulation Transfer Function

The Modulation Transfer Function (MTF) is a property of imaging systems. It is the transfer function of a lens: that is, it is the amplitude of the Fourier transform of the response of a lens to a point source. Ideally, this is flat, but due to diffraction and aberrations it decreases with increasing frequency in all optical systems. The MTF also depends on how far from the optical axis it is measured, and tends to be worse further off the optical axis.

Equivalently, the MTF is the response of an imaging system to a series of black and white bars at a given frequency: the contrast between white and black bars of the imaged system is equal to the MTF of the optical system.